20050325

Interference in Bose-Einstein CondensatesScienceJavanainencomments on nondestructive measurement of relative phase difference between two separated BECs, recently conducted by Sabaet al. within the Ketterle Group at MIT's Center for Ultra-Cold Atoms: "The experiments open up new ways to manipulate condensates, which are macroscopic objects, as if they were quantum mechanical entities. Measurement devices based on matter-wave interferometry are a potential application."

Quantum Interference in TimearXivPaulus has posted a preprint of the recent temporal quantum interference experiments, widely reported earlier this month: "The conceptually most important interference experiment is the double-slit scheme, which has played a pivotal role in the development of optics and quantum mechanics. [...] We have realized an intriguing implementation of the double slit in the time domain. The observation of interference and its absence at the same time for the same electron is a beautiful demonstration of the principles of quantum mechanics."

Gaidarzhy Defends Quantized DisplacementarXiv In cond-mat 0503502, Gaidarzhy et al.reply to Schwab's critical comments on the Mohanty Group's recently-reported experimental evidence of macroscopic quantum displacement in a nanomechanical oscillator: "In summary, both the objections and the premise of the comment, on the data interpretation, by Schwab et al. are not valid [...] A proper theoretical framework to understand quantized motion of a macroscopic mechanical system of 50 billion atoms, in presence of decoherence and dissipation, is yet to be developed."

20050318

Measurement Based Quantum ComputationVienna In Nature434, Waltheret al.report on the first experimental demonstration of Grover's search via one-way quantum computing on entangled photons. Following initialization of a highly-entangled 'cluster state,' irreversible single-qubit measurements are performed in a feedforward process that determines the output of the system. Raussendorf and Briegel's original paper is available via quant-ph 0010033.

AIST Quantum Cryptography ResearchTokyo ATIP QUIST reports that AIST, the Japanese National Institute of Advanced Industrial Science and Technology, is establishing a national research center in quantum cryptography and communications this spring under direction of Hideki Imai, University of Tokyo. "Hiroyuki Yoshikawa, Director of AIST, is aiming to establish world-class technology which will contribute to establishing global standards for cryptography technology and procedures for its evaluation."

20050311

Macromolecular Quantum InterferenceViennaArndt, Hornberger and Zeilinger provide a summary of recent progress in matter-wave interferometry, outlining near-term experimental objectives as well as theoretical developments towards understanding the mechanisms of decoherence. "In our view, matter-wave interferometry should be feasible for large objects such as proteins, small viruses and nanocrystals with atomic masses of up to 10^6 units. Extrapolating our results to bigger masses and higher temperatures, we believe that neither collisions nor thermal decoherence will be a problem in these cases. No fundamental limit of quantum interference is yet in sight, but much work still has to be done to prepare and manipulate coherent beams of supermassive particles. Carrying out such experiments will be a fascinating challenge."

DARPA Quantum NetworkHarvard/Boston/BBN Chip Elliot reports on the current status of the DARPA Quantum Network, in continuous operation since June 2004. "The DARPA Quantum Network is the world's first quantum cryptography network, and perhaps also the first QKD system providing continuous operation across a metropolitan area. Four more nodes are now being added to bring the total to 10 QKD nodes." This paper updates quant-ph 0412029 for the upcoming SPIE conference.

20050304

Quantum Interference in TimePhysicsWeb, SlashdotPaulus and colleagues have conducted a novel version of the double slit experiment, observing interference fringes with electrons passing through a double slit in time. Separated by femtosecond laser pulses, the 'slit' is composed of two maxima and one minima of the electric field. Slashdot notes several related articles on Zeilinger's interference experiments with fullerenes and biomolecules; see also the "delayed-choice quantum eraser" experiment by Shih and Kim.

Schwab comments on Phys. Rev. Lett. 94, 030402 (2005)arXiv In reply to the recent Gaidarzhy et al. report on "Evidence for Quantized Displacement in Macroscopic Nanomechanical Oscillators," Schwabet al.contend that the Letter contains order-of-magnitude omissions and inaccuracies counter to any interpretation of quantized macroscopic displacement: " ... the evidence, analysis, claims, and conclusions presented are contrary to expectations from fundamentals of quantum mechanics and elasticity theory, and [...] the method used by the authors is unsuitable in principle to observe the quantized energy states of a nanomechanical structure."